President Bush agreed yesterday to share civilian nuclear technology with India, reversing decades of U.S. policies designed to discourage countries from developing nuclear weapons.

The agreement between Bush and Indian Prime Minister Manmohan Singh, which must win the approval of Congress, would create a major exception to the U.S. prohibition of nuclear assistance to any country that doesn't accept international monitoring of all of its nuclear facilities. India has not signed the nuclear Non-Proliferation Treaty, which requires such oversight, and conducted its first nuclear detonation in 1974.

Participants in the discussions said there had been debate within the administration about whether the deal with India -- which built its atomic arsenal in secret -- would undercut U.S. efforts to confront Iran and North Korea over their nuclear programs. There were also concerns about how the agreement would be accepted in Pakistan, India's regional rival and an ally in the U.S. campaign against al Qaeda.

But supporters of the approach said it was an important part of a White House strategy to accelerate New Delhi's rise as a global power and as a regional counterweight to China. As part of the strategy, the administration is also seeking ways to bolster Japan's posture in the region.

The Bush administration, which had not expected to reach agreement on the matter until a future Bush visit to India, said it moved more quickly because it had secured commitments from New Delhi to limit the spread of nuclear materials and technology. The agreement does not formally recognize India as a nuclear power -- a status India had sought -- but it is a significant plum for the world's most populous democracy and cements India as a key strategic U.S. ally in Asia for the coming decades.

R. Nicholas Burns, undersecretary of state for political affairs, called the agreement "a major move forward for the U.S." and "the high-water mark of U.S.-India relations since 1947." Burns said the agreement, the subject of months of talks and six weeks of intense negotiations, is in line with "efforts that nuclear powers have taken to maintain a responsible policy in terms of nonproliferation."

But some nonproliferation specialists found the deal troubling.

"This is a stunning example of the Bush administration's policy of exceptionalism for friends at the cost of a consistent and effective attack on the dangers of nuclear weapons," said Daryl G. Kimball, director of the Arms Control Association.

According to a White House communique yesterday, Bush agreed that "India should acquire the same benefits and advantages" as other states with advanced nuclear technology. Bush vowed to "work to achieve full civil nuclear energy cooperation with India."

Under the terms of the deal, India agreed to place its civilian nuclear facilities -- but not its nuclear weapons arsenal -- under international monitoring and pledged to continue to honor a ban on nuclear testing. In return, it would have access, for the first time, to conventionalweapons systems and to sensitive U.S. nuclear technology that can be used in either a civilian or a military program. It could also free India to buy the long-sought-after Arrow Missile System developed by Israel with U.S. technology.

The agreement does not call for India to cease production of weapons-grade plutonium, which enables India to expand its nuclear arsenal.

The United States did not offer support for India's drive to become a permanent member of the U.N. Security Council, and the sides did not reach agreement on India's plan for a $4 billion pipeline delivering natural gas from Iran. The administration opposes the deal on grounds that it provides Iran with hard currency it can use for its own nuclear program.